Objective To determine the role of Ca2+ in LHRH release in vitro. ABSTRACT:In a previous study we have reported that cultured LHRH neurons derived from the olfactory placode of monkey embryos release LHRH into media in a pulsatile manner at approximately 50 min intervals (Neuroscience Abst. 272.4, 1994). To further study the mechanism of LHRH pulse generation, in this experiment we have examined the role of calcium in LHRH release. 1) Exposing the cells to a low Ca2+ (10 nM) buffer solution suppressed LHRH release, while exposure to normal Ca2+ solution (1.25 mM) maintained pulsatile LHRH release; 2) LHRH release from cultured LHRH cells was stimulated by the L-type Ca2+ channel stimulant, Bay K 8644 (1 M), while it was suppressed by the L-type Ca2+ channel blocker, nifedipine (1 M), but not by the N-type channel blocker, w-conotoxin (1 M); 3) The intracellular Ca2+ transporting ATPase antagonist, thapsigargin (10 M), appears to suppress LHRH release, while the intracellular Ca2+ stimulant, ryanodine (1 M) stimulated LHRH release. These results indicate that 1) release of LHRH is influenced by the presence of extracellular Ca2+, 2) Ca2+ enters into the cell via L-type channels, but not N-type channels, and 3) mobilization of the intracellular Ca2+ is important for LHRH release. Therefore, the presence of extracellular Ca2+ is essential for pulsatile LHRH release, and mobilization of intracellular Ca2+ appears to stimulate LHRH release. Keywords LHRH neurons, pulsatility, fetal monkeys, LHRH release in vitro, intracellular Ca2+